As is well known, the augmentor comprises a well known flameholder consisting of a pilot section centrally supported in the housing of the augmentor and carries a plurality of radially extending gutters. A pluality of sprayrings upstream of the flameholder serves to judiciously inject fuel in the engine's exhaust to be entrained in and ignited in the aerodynamic wake of the flameholder. The pilot section is designed to provide a recirculation zone to stabilize the burning characterstics of the fuel so as to sustain combustion and to propagate the combustion around the perimeter of the flameholder
The augmentor should be capable of actuation at any time within the flight envelope for the aircraft's mission. It has been known that under certain aircraft operating conditions ignition and/or sustained operation has not been successful.
The typical pilot section of the augmentor is either domed or "V" shaped and the apex faces the fuel being injected by the sprayring. After the fuel entrained air flows past the aft station of the pilot section, a portion of the fuel/air mixture migrates rearwardly relative to the flow of the engine's exhaust and recirculates inside the pilot section. The fuel entrained air is brought in close proximity to the igniter mounted in the pilot section. Unless the fuel/air mixture is within the proper proportions combustion will not ensue. It has been found that the mixture in the heretofore known designs has often been either too lean or too rich for ignition to ensue. Tests have shown that a pilot section incorporating this invention can accommodate operation over a much broader range of fuel-air mixture ratios at all operating conditions.
We have found that we can obviate the fuel/air mixture problem in the pilot section by locating an opening or slot for discretely flowing the fuel entrained air into the pilot section at a predetermined location and orientation relative to the igniter. In particular, in the dome-shaped (in cross section) pilot section the opening is located downstream of the leading edge of the flameholder but in proximity thereto. The opening is oriented so that its plane is in coincidence with the walls of the opening and is perpendicular to the engine centerline such that the flow admitted into the pilot section is tangential to the inner wall of the apex of the dome and spaced from the igniter so that the fuel/air mixture passes in proximity thereto. Tests have shown that a pilot section incorporating this invention forms a small recirculating zone adjacent the igniter and has proven to provide efficacious ignition characteristics.
By creating the circulating vortices described in the paragraphs above around the full circumference of the pilot section in accordance with this invention the stability of the pilot section can be improved. This invention contemplates, in addition to improving ignition, improving stability by locating openings as described above around the circumference of the pilot section in a plane perpendicular to the centerline of the pilot section. The openings are oriented such that the flow into the pilot section is introduced tangentially to the inside surface of the leading edge.
In certain heretofore known systems the augmentor incorporated a shroud surrounding the pilot section designed to profile the flow to achieve an improved aerodynamic recirculation zone. The shroud provided a flow path adjacent to the outer surface of the pilot section and directed the fuel entrained air in proximity to the aft end of the pilot section. Augmentors incorporating this design did not achieve the desired stability characteristics for all operating conditions.